The long-term goal of Project 2 is to elucidate the role of ribosomal protein L13a in post-transcriptional regulation of inflammatory gene expression in monocyte/macrophages. Interferon (IFN)-gamma is the classic activator of monocyte/macrophages; it induces rapid transcription of inflammatory growth factors, proteases, chemokines, and generators of radical species. If unregulated, this process becomes chronic and monocyte/macrophage products accumulate, damage host tissue, and contribute to chronic disorders of blood vessels, e.g., atherosclerosis. We have discovered a novel translational control pathway that acts as an endogenous regulator of the inflammatory response. In myeloid cells, IFN-gamma induces assembly of the IFN-Gamma-Activated Inhibitor of Translation (GAIT) complex, which binds an RNA element in the 3untranslated region of pro-inflammatory target mRNAs, and inhibits their translation. In Preliminary Studies we show that one GAIT protein, L13a, has a critical role in the GAIT system: its function is regulated by phosphorylation, it induces conformational changes in other GAIT proteins to regulate target mRNA recognition, and by interaction with eIF4G it is responsible for the observed translational silencing. Recently, we have shown that stress can alter GAIT system activity and influence inflammatory gene expression. Based on these results, we propose the following hypothesis: IFN-gamma-dependent phosphorylation of L13a induces a conformational change that facilitates its release from the 60S ribosomal subunit, formation of the GAIT complex, and binding to eIF4G to cause translational silencing of inflammatory transcripts; moreover, physiological stress can alter GAIT system function and inflammatory gene expression. We will test this hypothesis by pursuit of three Specific Aims. In Aim 1 we will determine the mechanism of inducible release of L13a from ribosome in the response to inflammatory stimulus. In Aim 2 we will determine L13a interactions required for GAIT complex assembly and silencing of inflammatory gene expression. In Aim 3 we will determine the mechanisms by which stress alters GAIT complex function and inflammatory gene expression.